Post-traumatic adjustment of pulse propagation in nerves with reduced excitability is a challenging biomedical and technological problem. In many cases such adjustments can be achieved with surgical interventions. However, surgery does not necessarily restore nerve conductivity to its pre-trauma levels, therefore still impaired conduction may cause partial or complete muscular paralysis. In this case propagation of excitation waves can be enforced only by applying external functional electrical stimulation (FES) using implantable [1] or surface stimulation electrodes [2-4]. This method has been confirmed as an effective tool for restoration of movement of paralyzed muscles in individuals with variety of neurological impairments [5].
Computerized systems for control of FES can deliver sequences of electrical stimuli with different frequency, amplitude and duration [6]. Commonly, these systems include variety of control units and electrical leads with multiple array or patch type stimulation electrodes. These electrodes deliver programmable stimuli, which are designed to maximize the effect of stimulation based on configuration of a particular stimulation field [7-10].
Successful FES process of functional restoration of muscle contraction depends on ability of nerve tissue to adequately conduct action potential. It also depends on excitation-contraction coupling in neuromuscular junctions, which transmit nervous impulses to muscular fibers. If any of these steps is impaired muscle does not contract normally. Usually, after severe neuromuscular injuries nerve conductivity is significantly reduced which, in turn, prevents the passage of excitation waves through neuromuscular transmitters. Under these circumstances propagation of excitation pulses is marginally stable and implementation of FES necessitates a significant increase of frequencies and amplitudes of functional electrical stimuli. The latest, instead of stabilization of propagation, can facilitate conduction blocks and may completely disrupt the process of training paralyzed muscles.
Accordingly, there is a need for new methods, systems and apparatus for stimulating excitable tissues which treat the problem of conduction instability and blockage therein.